Slight idle misfire

[cosbysweater]

Hey guys I have a question I just picked up a typhoon that had been sitting since about 2006. Before I bought it I found it had a dead fuel pump so I got a replacement pump for it and cleaned the terminals on the sending unit and got it running. It has higher milage but it was a daily driver. I bought it from someone who takes very good care of their cars so I wasn't worried about the mileage. I changed the oil before I fired it up. I drove it home and other then the suspension and tires being worn out it drove great. I did the plugs, wires, cap, rotor and fuel filter. The icm had been replaced so I left it. I noticed that although the vacuum gauge is stable the tach bounces a little bit. I pulled the injector plugs individually and found number 4 to not change the way the engine ran. I removed the injectors and upper intake and got the injectors cleaned and they were in very good shape. I reassembled and am still having the same symptom on number 4. I'm going to check compression and leak down on it. On the starter the engine sounds perfect with the injectors disconnected it is hitting on all cylinders and doesn't have the sound of a dead hole. Like I said the car drives perfect once you start driving it. It even sounds good out the tail pipe when idling. I'm wondering if these do have issues with stuck or burnt valves or if this is just a normal running characteristic of the engine. I'm going to do a leak down tonight and compression test. No blowby out the breather with the pcv hose crimped off so I'm leaning towards a top end issue. I'll post a video later. Thanks for any insite guys.

 

[QWERTYphoon]

you say the injectors were cleaned, but do you measure the resistance? they should all be about the same. Change your memcal out with a working truck, because they go bad. Change injector from 4 to 3, any change? What is your compression test telling you?

 

[Slyclone]

Burnt plug wire conducting. Look into the plug wires. Misses during idle?

Get a old empty spray bottle and mist the wires with some water see if the arc jumps from any of the plug ends.

I had a typhoon run a little funny could never figure it out. Ended up being #1 plug boot end was melted and you couldn't see it at all. Under high heat condition they melt. Some spend a extra hundred on wires, others but the protective boots and well some just pay the price. I still have the wire as a reminder of how much the truck can torture you.

Not saying it's your problem but it's one I encountered before and just suggested to check it out.

 

[cosbysweater]

the guy i sent the injectors too measured coil resistance and installed new filters and sonic cleaned them. luckily i found the issue last night. i checked the wires for arching and they were good, i installed heat sleeves on all the plug wires and routed them away from the exhaust as much as i could. the compression was extremely good, i had 150 on the passenger side bank on all the cylinders, i swapped plugs around to make sure i didnt crack any of them on install. what i found was the lower intake gasket was blown out on the number 4 cylinder! i didnt see it when i had the upper plenum off and i must have missed it when i did my initial brake clean test. i checked the map and coolant temp sensor and they are all within spec just to be sure. Its one of those things where these older cars bring you back down to earth and you have to rely more on the basics and caveman diag techniques. haha